Question

In JAVA

How can you multiply two matrices that are different lengths.

the answer should be in 3d array so [][][]

how to multiply a 3d array with a 2d array and the result is in 3d array

for example:

double[][][] nums1 = { { {0.0, 0.1, 2.0}, {3.0,4.0,5.0} },

{ {6.0,7.0,8.0}, {9.0,10.0,11.0} } }

int [][] nums2 = { {1,2,3}, {4,5,6}, {7,8,9}}

and the results should be in [][][] <-- in this dimension

int[][][] answer = { {  {18, 21,24}, {54,66,78} },

{ {90, 11, 132}, {126,156,186} } }

Thanks !

Answer 1

import java.util.Random;


public class MatrixMultiplication {
        
        public static double[][] multiplyMatrix(double a[][], int b[][]) {
                
                if(a[0].length != b.length) {
                        throw new IllegalArgumentException("Matrix size is not allowed for multiplication");
                }
                
                double product[][] = new double[a.length][b[0].length];
                // multiply both matrix
                for (int i = 0; i < a.length; i++) {
                        for (int j = 0; j < b[0].length; j++) {
                                for (int k = 0; k < b.length; k++) {
                                        product[i][j] = product[i][j] + a[i][k] * b[k][j];
                                }
                        }
                }
                
                return product;
        }

        public static void printMatrix(double mat[][]) {
                for (int i = 0; i < mat.length; i++) {
                        for (int j = 0; j < mat[i].length; j++) {
                                System.out.printf("%10.2f", mat[i][j]);
                        }
                        System.out.println();
                }
        }

        public static void main(String[] args) {
                double[][][] nums1 = { { {0.0, 0.1, 2.0}, {3.0,4.0,5.0} },
                                { {6.0,7.0,8.0}, {9.0,10.0,11.0} } };
                int [][] nums2 = { {1,2,3}, {4,5,6}, {7,8,9}};
                
                double [][][] result = new double[nums1.length][][];
                for(int i=0; i<nums1.length; i++) {
                        result[i] = multiplyMatrix(nums1[i], nums2);
                        printMatrix(result[i]);
                        System.out.println();
                }
                
        }
}

**************************************************
So, I have take a 2D matrix from 3D matrix, and then created the array which contains the 2D matrices in a 3D matrix.

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